list-objects-filter: add and use initializers

In 7e2619d8ff (list_objects_filter_options: plug leak of filter_spec
strings, 2022-09-08), we noted that the filter_spec string_list was
inconsistent in how it handled memory ownership of strings stored in the
list. The fix there was a bit of a band-aid to set the "strdup_strings"
variable right before adding anything.

That works OK, and it lets the users of the API continue to
zero-initialize the struct. But it makes the code a bit hard to follow
and accident-prone, as any other spots appending the filter_spec need to
think about whether to set the strdup_strings value, too (there's one
such spot in partial_clone_get_default_filter_spec(), which is probably
a possible memory leak).

So let's do that full cleanup now. We'll introduce a
LIST_OBJECTS_FILTER_INIT macro and matching function, and use them as
appropriate (though it is for the "_options" struct, this matches the
corresponding list_objects_filter_release() function).

This is harder than it seems! Many other structs, like
git_transport_data, embed the filter struct. So they need to initialize
it themselves even if the rest of the enclosing struct is OK with
zero-initialization. I found all of the relevant spots by grepping
manually for declarations of list_objects_filter_options. And then doing
so recursively for structs which embed it, and ones which embed those,
and so on.

I'm pretty sure I got everything, but there's no change that would alert
the compiler if any topics in flight added new declarations. To catch
this case, we now double-check in the parsing function that things were
initialized as expected and BUG() if appropriate.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 11 insertions, 9 deletions

diff --git a/list-objects-filter-options.c b/list-objects-filter-options.c
index 18c51001dc..56a1933a50 100644
--- a/list-objects-filter-options.c
+++ b/list-objects-filter-options.c
@@ -108,7 +108,7 @@ int gently_parse_list_objects_filter(
 
 	strbuf_addf(errbuf, _("invalid filter-spec '%s'"), arg);
 
-	memset(filter_options, 0, sizeof(*filter_options));
+	list_objects_filter_init(filter_options);
 	return 1;
 }
 
@@ -223,8 +223,7 @@ static void transform_to_combine_type(
 		struct list_objects_filter_options *sub_array =
 			xcalloc(initial_sub_alloc, sizeof(*sub_array));
 		sub_array[0] = *filter_options;
-		memset(filter_options, 0, sizeof(*filter_options));
-		string_list_init_dup(&filter_options->filter_spec);
+		list_objects_filter_init(filter_options);
 		filter_options->sub = sub_array;
 		filter_options->sub_alloc = initial_sub_alloc;
 	}
@@ -255,11 +254,8 @@ void parse_list_objects_filter(
 	struct strbuf errbuf = STRBUF_INIT;
 	int parse_error;
 
-	if (!filter_options->filter_spec.strdup_strings) {
-		if (filter_options->filter_spec.nr)
-			BUG("unexpected non-allocated string in filter_spec");
-		filter_options->filter_spec.strdup_strings = 1;
-	}
+	if (!filter_options->filter_spec.strdup_strings)
+		BUG("filter_options not properly initialized");
 
 	if (!filter_options->choice) {
 		string_list_append(&filter_options->filter_spec, arg);
@@ -346,7 +342,7 @@ void list_objects_filter_release(
 	for (sub = 0; sub < filter_options->sub_nr; sub++)
 		list_objects_filter_release(&filter_options->sub[sub]);
 	free(filter_options->sub);
-	memset(filter_options, 0, sizeof(*filter_options));
+	list_objects_filter_init(filter_options);
 }
 
 void partial_clone_register(
@@ -429,3 +425,9 @@ void list_objects_filter_copy(
 	for (i = 0; i < src->sub_nr; i++)
 		list_objects_filter_copy(&dest->sub[i], &src->sub[i]);
 }
+
+void list_objects_filter_init(struct list_objects_filter_options *filter_options)
+{
+	struct list_objects_filter_options blank = LIST_OBJECTS_FILTER_INIT;
+	memcpy(filter_options, &blank, sizeof(*filter_options));
+}